1. Field of the Invention
The present invention relates to a viscoelasticity measuring device to measure viscoelasticity properties and particularly to a viscoelasticity measuring device to measure viscoelasticity properties by imparting a displacement profile to a sample presser.
2. Description of the Related Art
Conventionally, there have been various methods proposed to measure viscoelasticity. As a means for conducting a measurement of static viscoelasticity, there are, for example, a stress relaxation measuring method in which a certain strain is imparted to a sample to measure a changing stress, a creep measuring method in which a certain stress is imparted to a sample to measure a changing strain, a stress/strain measuring method in which a certain strain speed is imparted to a sample, etc.
As a means for conducting a dynamic viscoelasticity measurement, there are Torsion-pendulum method (ISO6721 part 2, JIS K7244-2), Flexural vibrationxe2x80x94Resonance-curve method (ISO6721-3), Tensile vibrationxe2x80x94Non-resonance method (ISO6721-4), Flexural vibrationxe2x80x94Non-resonance method (ISO6721-5), Shear vibrationxe2x80x94Non-resonance method (ISO6721-6), Torsional vibrationxe2x80x94Non-resonance method (ISO6721-7), and so on.
These measuring processes are being used in the field of semiconductor manufacturing; for example, in the measurement of the viscoelasticity properties of an abrasive cloth used for polishing semiconductor wafers or the like.
Such abrasive cloths used for polishing semiconductor wafers are in general made of polymeric materials of various properties and structures, including polyester non-woven cloths or foam polyurethane sheets.
The mechanical properties and particularly viscoelastic behaviors of such abrasive cloths can seriously affect the distribution of pressure exerted to materials to be polished (such as semiconductor wafers) to such an extent it is known that the materials, structures and viscoelastic properties after aging of the abrasive cloths influences the abrasive accuracy of the materials to be polished.
Therefore, abrasive cloths have so far been subjected to various viscoelasticity measurements.
Conventionally and in general, the viscoelasticity measurement of the abrasive cloths used for polishing the semiconductor wafers or the like was conducted on the basis of the measurement of hourly change in their deformation, that is, a creep deformation of the abrasive cloths was measured under a certain load thereof.
In the static measurement, however, it was impossible to realize conditions for imparting a forced displacement in an extremely short time and eliminating the conditions in an extremely short time in the static measurement and to conduct measurements under repeated loads other than stable vibrations in the creep measurement.
On the other hand, the behaviors of the abrasive cloths observed at the time of actual abrasion works are repeated in the form of forced displacement and recovery. Therefore, a means for measuring the viscoelasticity of the abrasive cloths under the condition similar to the actual behaviors of the abrasive cloth during the abrasion operation has long been wished for.
As one means for measuring the viscoelastic behaviors of abrasive cloths used for polishing semiconductor wafers or the like, the forced displacement measuring method may be considered. Therefore, the case of conducting measurements by the forced displacement measuring methods will be explained referring to FIG. 5, which shows the general structure of the conventional measuring device.
In the figure, the numeral 21 denotes a stage which is adapted to vertically move and support a sample 22 thereon. Above the sample 22, there is provided a rod 23 with an upper end portion thereof secured and a lower end face thereof attached with a load cell 24. Upon the upper surface of the sample 22, there is provided a presser 25 adapted to press the sample 22, the presser having an upper end portion adapted to contact the load cell 24.
Further, the stage 21 is attached with a stand 26, which has a tip portion provided with a laser displacement meter 27 to indicate the displacement of the sample 22 by measuring the displacement of the presser 25.
Then, the above arrangement is adapted to obtain viscoelastic properties by placing the sample 22 on the stage 21 and the presser 25 on the sample 22. At this time, care is to be taken to bring the upper portion of the presser 25 into contact with the load cell 24. Thus arranged, the laser displacement meter 27 is subjected to an origin correction such that the resultant position is defined as an origin thereof.
Thereafter, the stage 21 is vertically reciprocated to displace the same such that the measurement is started. The displacement of the sample is measured by the laser displacement meter 27. In addition, the load generated by the displacement and applied to the sample 22 by the presser is measured by the load cell 24.
Then, the stress generated in the sample is sought in addition to obtaining the displacement. More specifically, the measurement result of the viscoelasticity properties of the abrasive cloth used for polishing the semiconductor wafer is shown in FIG. 6.
As will be understood from the FIG. 6, the viscoelasticity properties of the abrasive cloth indicates that an increased displacement causes an increased stress to such an extent that the stress reducing to nil will not reduce the displacement to nil.
In this connection, there is a problem that the FIG. 5 device compresses the sample (the abrasive cloth) but will not cause no immediate displacement the moment a load is applied due to a problem of accuracy concerning the speed and position controls of the vertical stage reciprocation because of the vertical mechanism used in the stage.
Particularly, as the stress increase is limited at the time of the compression (or displacement), there remains a technical problem that the result is different from the viscoelastic properties under the actual use conditions.
In this way, the device fails to offer the displacement profile equal to that under a condition similar to the actual use conditions with the result that the technical problem means it is impossible to measure viscoelastic properties under a condition close to the actual use conditions.
The present invention is directed to solving the above described technical problems and to provide a viscoelasticity measuring device which imparts a desired displacement profile to a sample such that its viscoelastic behaviors under a use condition close to the actual use conditions.
The viscoelasticity measuring device according to the present invention which imparts a sample a predetermined displacement to measure a resultant displacement and stress comprises a presser to impart displacements to a sample; a rod to convey the displacements to the presser; a control jig kept in contact with an upper end portion top of the rod and adapted to move to impart a desired displacement to the rod; a load cell which detects a load exerted to the sample to detect a stress generated in the sample; and a displacement sensor to detect the displacement of the sample; the displacements imparted to the sample being defined in accordance with a configuration and a moving speed of the control jig.
In this way, as the displacement imparted to the sample is defined by the configuration of the control jig and its moving direction, the movement of the control jig will impart the displacement profile to the sample.
Therefore, the elimination of vertical movement as done in a stage in the conventional device will minimizes the adverse effect of inertia such that precise speed and position controls are ensured. As a result, it is possible to impart a desired displacement to the sample and measure viscoelastic behaviors under conditions close to actual use conditions.
Here, it is preferred that a predetermined displacement is imparted to the sample by defining a desired configuration to be imparted to the sample by means of the control jig while allowing the control jig to move at a predetermined moving speed in a plane perpendicular to an axis of the rod.
It is to be noted that a configuration of the control jig can produce different displacement profiles depending on the moving speed thereof. Therefore, it is preferred that not only the configuration of the control jig but also the moving speed is defined in order to impart the sample a predetermined displacement profile.
For example, it is possible to measure the viscoelastic properties under a condition imparting a forced displacement in an extremely short time or a condition removing a displacement imparted in an extremely short time by allowing the control jig at a high speed.
Further, it is preferred that the control jig is adapted for reciprocal movement, the reciprocal movement of the control jig repeatedly imparting forced displacements to the sampler and releasing the load therefrom.
In this way, it is possible to measure the viscoelastic properties under a condition imparting repeated loads to the sample because the control jig is adapted for reciprocal movement to impart repeated loads to the sample.
Then, it is preferred that the control jig is adapted to provide a configuration to define the displacements to be imparted to the sample, the control jig being adapted to move in a plane perpendicular to an axis of the rod at a predetermined speed such that the desired displacements are imparted to the sample.
It should be born in mind that even if the control jig has a similar configuration, the displacement profile imparted to the sample can differ depending upon the moving speed thereof. It is therefore preferred in order to impart a predetermined profile to the sample that not only the jig configuration but also the moving speed is defined. For example, a high speed movement of the jig ensures that the measurement of viscoelasticity is made possible under conditions imparting a forced displacement in an extremely short time or conditions eliminating the displacement imparted in an extremely short time.
Further, it is preferred that the control jig is adapted for reciprocal movement, the reciprocal movement of the control jig repeatedly imparting forced displacements to the sample and a release of load therefrom.
In this way, the control jig adapted for reciprocal movement and repeatedly imparted load to the sample ensure that the measurement of viscoelasticity under a condition imparting repeated displacements is conducted.
Further, it is also preferred that the control jig has a configuration to define the displacements to be imparted to the sample, the configuration having a portion which will not induce vertical actuation of the rod.
In this way, the provision of the portion which will not induce vertical actuation of the rod prevents the rod from stopping the movement during the course of the configuration of the jig such that the accurate repetition of the rod displacements is ensured. In other words, if the non-load condition and/or the maximum load condition reached at the portion which will not induce vertical actuation of the rod, an accurated condition can be brought about.
Here, it is preferred that the portion which will not give a (viz., induce or cause) vertical actuation of the rod is formed at opposite ends of the configuration of the control jig to define the displacements and in a plane parallel to the moving direction of the control jig.